A kitchen water purifier has found its way into every family. To solve a problem that water production of the water purifier is little, water outflows slowly, and hence a large amount of water required by family life cannot be satisfied, a water purifier with a water bag function appears. The water purifier with the water bag function, i.e. a water bag type water purifier, is characterized in storing produced water in the water bag. A water capacity of the water bag depends on an overall structure of the machine and a volume of the water bag. The water in the water bag can be used directly when a user intends to use water, and water is produced by a filter cartridge when the water bag is empty. Thus, it is a key technique for the water bag type water purifier to judge whether the water bag is full of the produced water by detecting pressure of the water bag.
However, the water bag type water purifier in the related art is not accurate in terms of detecting the pressure of the water bag, and a case that even if the water bag is full, the water is still produced by the filter cartridge and is filled into the water bag often happens, thereby leading the water bag to break down, or even causing a burst in a serious case. A danger coefficient is high and a potential safety hazard is left to the user.